Many hydrophilic polymers are highly biocompatible, and thus such polymers, including biopolymers and synthetic polymers, have been widely used in the field of medicine. In particular, since biopolymers are main biological constituents, they are highly biocompatible in many cases. In addition, each biopolymer has peculiar physiological functions. Therefore, biopolymers are applied to drug delivery carriers, matrices for tissue construction, material-surface-coating materials, and the like in the field of medicine. However, many such hydrophilic polymers are water soluble. In general, a hydrophilic polymer is allowed to contain a poorly water-soluble compound by a method comprising: dissolving a hydrophilic polymer and a poorly water-soluble compound in water; allowing the compound to be immersed in water contained in the hydrophilic polymer; and using the resultant directly as a substrate (matrix) or drying it before use. According to such method, when a hydrophilic matrix contains a poorly water-soluble compound at a concentration higher than that corresponding to the solubility of the poorly water-soluble compound in water, the poorly water-soluble compound is precipitated in the hydrophilic matrix. Therefore, it is difficult to allow a hydrophilic matrix to contain a poorly water-soluble compound at a high concentration. Also, in general, when a hydrophilic matrix is allowed to contain a poorly water-soluble compound, a poorly water-soluble compound is water-solubilized with the use of a surfactant. In such case, if the surfactant content is large, chemical, physical, and optical properties of such a contained compound might change. Further, in terms of in vivo use, the toxicity of a surfactant might be observed, which is problematic. Therefore, a technique for allowing a matrix to contain a poorly water-soluble compound without surfactant or with a small amount of surfactant is very important not only in the field of medicine but also in fields involving the use of poorly water-soluble compounds (e.g., pigments) in a dispersed state.
Poorly water-soluble immunosuppressive agents (e.g., sirolimus) and anticancer agents (e.g., paclitaxel) are used as drugs for drug-eluting stents (DESs) that have been significantly developed in recent years. At present, nondegradable synthetic polymers are used for a matrix capable of containing such a drug. However, inflammation caused by long-term application of such a matrix is a matter of concern, and thus a biodegradable matrix is necessary. When collagen is used for a biodegradable hydrophilic matrix, it is difficult to allow collagen to contain a drug as described above. Therefore, a collagen matrix layer and a drug layer are alternately laminated for drug coating so that a collagen matrix does not contain such a drug (Non-Patent Document 1).
1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) can dissolve protein such as collagen and gelatin, and thus it is used for production of a matrix for tissue construction (Patent Document 1) and production of a fibrous matrix by electrospinning (Patent Documents 2 and 3). However, the documents mainly focus on production of a matrix itself. None of the documents describe the inclusion of a poorly soluble compound in such a matrix or the state of the drug in the matrix.
In addition, Patent Document 4 discloses, as an emulsion vehicle containing an insufficiently soluble drug, a pharmaceutical composition containing a therapeutic agent with a low solubility, at least one type of tocol, at least one type of solvent adjuvant, and at least one type of surfactant. However, the document does not describe that a poorly water-soluble compound is contained in a hydrophilic matrix in a finely-dispersed state.    Non-Patent Document 1: Journal of Controlled Release 108, 178-189, 2005    Patent Document 1: JP Patent Publication (Kohyo) No. 2002-531182 A    Patent Document 2: JP Patent Publication (Kohyo) No. 2004-532802 A    Patent Document 3: JP Patent Publication (Kokai) No. 2004-321484 A    Patent Document 4: JP Patent Publication (Kohyo) No. 2003-500368 A